Modeling of two-phase CO₂ ejectors using an Eulerian–Eulerian two-fluid approach.

Ejector is a work recovery device that plays a critical role in increasing the overall efficiency of CO2 heat pump systems. Despite extensive research, persistent challenges in the numerical modeling of these devices limit the effective use of simulations as reliable and cost-efficient tools for design and optimization. These challenges are linked to the complex non-equilibrium two-phase and turbulent flow, with the presence of flashing phenomenon, rapid phase changes and compressibility effects. This study introduces an open-source numerical model based on the Eulerian–Eulerian two-fluid framework within OpenFOAM, which captures the detailed phase interactions and non-equilibrium effects often overlooked in previous models. Moreover, the model incorporates polydispersity to more realistically simulate phase change during flashing in the motive nozzle—an aspect not considered in previous CO2 ejector models. To ensure consistent performance of the model across a range of operating conditions, 19 different cases with both supercritical and subcritical (including subcooled) motive flows are simulated and compared to independent experimental data. The model shows consistent predictions with an average deviation of approximately 8%, 12%, and 6% in predicting motive mass flow rate, suction mass flow rates, and entrainment ratio, respectively. This open-source model is expected to contribute to better designs of CO2 ejectors and improved operational efficiencies of CO2 heat pumps.